Semiconductor lasers are well known devices in which the injection of charge carriers across one or more semiconductor junctions results in stimulated emission of radiation. Mirrored facets on the device are provided to form a cavity in which the stimulated emission will produce lasing in an active layer when the injected current density is above a certain threshold level. High output power operation of these devices is limited by the susceptibility of the mirror facets to catastrophic damage when illuminated at high intensity.
High power semiconductor lasers in the prior art generally had broad emitting areas to spread the optical field. This reduced the intensity incident on the mirror facets to prevent facet damage. However, such devices often suffered from a lack of control over oscillation of lateral modes in the junction plane. This could lead to filamentation and self-focussing, producing unsatisfactory variations in the far-field intensity distribution pattern. A further disadvantageous result of uncontrolled lateral modes was non-linearities or "kinks" in the relation between current and output flux.
Another prior art attempt to produce a high power device used an array of narrow stripes to laterally confine charge carrier flow. Stripe widths of about 3-5 .mu.m inhibited oscillation in unwanted lateral modes, while the device operated as an array of many low power lasers. By closely packing the stripes with center-to-center spacing of 8-15 .mu.m, some interaction of the optical evanescent fields from neighboring stripes could be achieved. Examples of these devices are described in papers by Scifres, et al. (Applied Physics Letters, Vol. 33, No. 12, December 1978) and Tsang, et al. (Applied Physics Letters, Vol. 34, No. 2, January 1979). However, these devices suffered the disadvantages that individual lasing regions did not begin to lase, or "turn on", simultaneously when a current pulse was injected. This could cause an unstable far-field pattern during the turn on period. Another disadvantage was that coupling between lasing regions tended to diminish at high driving currents.
A variation of the closely packed stripe array device used curved conducting contacts to connect the stripes in the array. As reported by Scifres, et al. (Applied Physics Letters, Vol. 34, No. 4, February 1979), this improved the coupling between stripes, reducing the severity of the disadvantages. However, these devices still suffered from non-simultaneous turn on and loss of coupling at high driving currents.